Radar detectors for detecting police radar are well known. Many such radar detectors are sold by BEL-Tronics Company in association with its trade marks BEL.RTM., VECTOR.RTM., FMT.RTM., FMT-FUNDAMENTAL MIXER TECHNOLOGY.RTM., RSV.RTM., SHADOW TECHNOLOGY.RTM., among others; and a number of features of those radar detectors are such as those taught in U.S. Pat. Nos. 4,571,593, 4,952,936, and 4,961,074.
Presently, a new series of radar detectors is under development by BEL-Tronics Company, and they include image rejection mixers of the sort taught in co-pending U.S. patent application Ser. No. 09/097,261 filed Jun. 15, 1998.
Among the teachings of the co-pending application noted above, certain circuits are shown for the front end of broad band, multi-band radar detectors. The radar detectors of the present invention may utilize front ends such as those taught in the co-pending application; and the platform for such radar detectors as taught in the present application is therefore essentially the same as for radar detectors incorporating image rejection front ends as noted immediately above.
It is well known that any high frequency operating device, especially those which incorporate free running, wide band, voltage tuned oscillators, are subjected to inaccuracies due to drift, which may occur over time, or which may also occur as the ambient temperature in which the device is operating changes. If sufficient drifting occurs, then it is possible that the radar detector might not even be able to detect the presence of radar frequencies in one or more particular radar frequency bands of interest.
Radar detectors which utilize a swept frequency first local oscillator have the disadvantage that there may be poor frequency stability over time and temperature. Thus, in order that there is reasonable assurance that the radar detector will tune to any desired radar frequency band, the frequency of the swept first local oscillator should be controlled to a high degree. However, this is generally not possible; and therefore, a broader swept frequency band must be implemented. As a simple example to explain the importance of controlling the frequency of the swept first local oscillator, and for ease of understanding of the mathematics involved, a radar detector having a first local oscillator frequency of 10 GHz may be considered. The first local oscillator frequency of the postulated radar detector sweeps a radar band having a 100 MHz bandwidth. Obviously, the radar detector will not sweep any portion of the required bandwidth if the center frequency of the local oscillator changes by more than 1%--that is, if the local oscillator frequency changes by more than 100 MHz. Of course, in practise is it desirable to maintain the frequency of the swept first local oscillator to within .+-.0.1% of the nominal first local oscillator frequency, so as to prevent the oscillator frequency from drifting so far as to cause a loss of band coverage of any desired radar frequency band. To compensate for a possible drift of even 0.1%. it is therefore necessary to sweep the frequency of the first local oscillator an additional 10 MHz on either side of the band limit so as to ensure complete coverage of the desired radar frequency band at all times. However, it is virtually impossible to hold a swept local oscillator, particularly one operating in a multi-gigahertz frequency band such as about 10 GHz, or about 15 GHz in a more practical example, to maintain a tolerance of .+-.0.1% over time and when it may be exposed to a wide range of temperatures. This is, of course, particularly true in respect of a free running, wide band, voltage tuned local oscillator.
The present invention provides a means by which a high accuracy setting of the first local oscillator frequency may be established. This is discussed in greater detail hereafter. However, as will also be discussed hereafter, implementation of the high accuracy control of the first local oscillator frequencies comes as a consequence of incorporating into the platform of the radar detector a second local oscillator which is synthesized from a crystal reference so as to provide a high accuracy source of gigahertz frequency. Moreover, the second local oscillator, being a synthesized frequency local oscillator, has its frequency governed by a phase lock loop feedback circuit which, itself, is under the control of a microprocessor which is found in the radar detector. Thus, the output frequency of the synthesized frequency second local oscillator may be varied, and this gives rise to a radar detector wherein the tuning range in each frequency band of interest may be increased by an amount equal to the adjustment amount by which the frequency of the synthesized frequency second local oscillator may be adjusted. The adjustment amount must not exceed the first intermediate frequency bandwidth. This feature is discussed in greater detail hereafter.
On method for the calibration configuration scheme of the present invention to become operative is a feature of this invention. That is that the radar detector may change its configuration from a triple conversion radar detector to a dual conversion radar detector. In so doing, the second mixer is bypassed, by operation of a pair of single pole, double throw switches which are located one at each side of the second mixer, as described in greater detail hereafter.
In any radar detector, there may be mixing between the frequency components of the various local oscillators, particularly between the second local oscillator and the first local oscillator. This may often give rise to spurious responses which are undesirable because they may suggest that a radar signal in a particular band of interest may be present when, in fact, it is not. Various steps are taken to overcome the incidence of undesirable spurious responses, which steps are beyond the scope of the present invention. However, the inventor herein has determined a mechanism by which the spurious responses that occur may, in fact, be taken advantage of under controlled conditions. It is this fact which leads to the capability of radar detectors in keeping with the present invention to be self-calibrating at any instant in time, either under the control of the user or under self-control as determined by the microprocessor controller which is found in the radar detector. Thus, much greater accuracy of tuning, and control of drift due to passage of time or due to changes in ambient temperature, may be achieved in keeping with the present invention.
It is therefore an object of the present invention to provide a broad band, multi-band radar detector wherein the tuning range of the radar detector may be increased in each frequency band of interest by adjustment of the synthesized frequency second local oscillator which is found in the radar detector.
A further object of the invention is to provide such a radar detector as noted above, wherein one or another of three predetermined intermediate frequency signals may be obtained from the first mixer of the radar detector.
Yet another object of the present invention is to provide a broad band, multi-band radar detector which may be configured so as to function either as a triple conversion radar detector or as a dual conversion radar detector.
Still a further object of the present invention is to provide a radar detector which may function as a triple conversion radar detector or a dual conversion radar detector, which may be controlled so that, when the radar detector is functioning as a dual conversion detector, a third intermediate frequency may be output from the first mixer.
A still further purpose of the present invention is to provide a radar detector in which, by controlling the frequency of the synthesized frequency second local oscillator while the radar detector is functioning in a dual conversion mode, the radar detector may be calibrated so as to more accurately control the frequency of the swept frequency first local oscillator.
Yet a further object of the present invention is to provide a radar detector where either of the first or second local oscillators may be controlled, while the other second or first local oscillator is at a fixed frequency, so as to calibrate the radar detector to more accurately control the frequency of the swept frequency local oscillator.
A further object of the present invention is to provide methods by which a broad band, multi-band radar detector may be calibrated.